1. Field of the Invention
The present invention relates to cutting elements on a drill bit. More particularly, the present invention relates to polycrystalline diamond compact cutters on a drill bit. Even more particularly, the present invention relates to polycrystalline diamond compact cutters having different zones of thermal stability and hardness.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Polycrystalline diamond compact (PDC) cutters are used in drilling operations for oil and gas. Prior art drill bits were roller cone bits with multiple parts and rotating surfaces to grind through the rock formation. Newer drill bits were fixed-head bits, which were composed of a single part without any moving components. The fixed-head bits could be rotated by the drill string, so additional moving parts on the bit were not needed. Cutters attached to a fixed-head surface grind through a rock formation. The fixed cutters were more reliable under extreme heat and pressure conditions of the wellbore because there were no moving components. However, the wear on these cutters was substantial. The material composition of the cutters has evolved to extend the working life and to increase productivity of the cutters.
Diamond is the hardest material known, so cutters of diamond composition have been pursued. Bonding diamond to metal is a challenge, so the drill bits evolved from steel to composite materials, in particular, tungsten carbide. Tungsten carbide composite readily bonds to diamond. The basic prior art cutter is comprised of a diamond table made from diamond grit with a formation agent and a substrate of tungsten carbide. The formation agent is a metallic binder, usually cobalt. The diamond grit is sintered under high temperature and high pressure conditions, forming a layer bonded to the tungsten carbide or other substrate with the formation agent as a catalyst. The High Temperature-High Pressure (HT-HP) press can form the layer with a Cobalt or other Group VIII element as the catalyst, and the properties of the layer have been modified for various thicknesses, profiles, and patterns to affect the working life of the cutters. Alternatively, the diamond table can be sintered and removed from the substrate. The diamond table as a disk can undergo leaching for the removal of metal content, without the substrate. Then, the leached disk can be replaced on a substrate to form a cutter. The formation agent, such as a cobalt compound, is the binder in this formation of a cutter.
PDC cutters face additional problems, during drilling operations in the oil and gas industry. Down the wellbore, the drilling conditions are extreme. There can be excessive heat, over 750 degrees Celsius, which causes thermal expansion of the diamond-binder bond in the diamond table. The PDC cutter weakens when the binder expands and the diamond table is less stably mounted on the substrate. The diamond surface is more likely to become damaged or dislodged from the substrate. The PDC cutter is tough, but limited by thermal expansion problems.
The prior art has further modified PDC cutters, according to the limitations of the diamond-binder bond. For example, once sintered to the tungsten carbide substrate, the Cobalt binder can be removed from the diamond table in a process called “leaching”. The PDC cutter lasts longer without as much thermal expansion, but the PDC cutter fractures more easily. Adjusting for the thermal stability, the PDC cutter loses toughness.
Various patents and patent applications disclose selective leaching to form layers of different thermal stability and toughness. Various shapes of the layers at various depths are also disclosed.
United States Publication No. 20140166371, published for Whittaker on Jun. 19, 2014, and United States Publication No. 20110056141, published for Miess, et al. on Mar. 10, 2011, both disclose methods for selective leaching. There can be a deep leach or a shallow leach. Masking can be used to set the layers so that the Cobalt or other binder can be removed at different rates and depths in the diamond table. Various shapes and patterns are disclosed as possible with this method. Besides masking, other additives can be added to form the desired pattern of leached diamond composite. United States Publication No. 20140069726, published for Mumma, et al. on Mar. 13, 2014, discloses a hydrophile additive.
Other patents disclose a particular arrangement of layers. U.S. Pat. No. 8,197,936, issued to Keshavan on Jun. 12, 2012, discloses a first thermally stable polycrystalline diamond layer, a second carbide substrate layer, and a third polycrystalline cubic boron nitride layer. The layers are in a particular configuration with the third layer surrounded by the first and second layer. U.S. Pat. No. 8,567,531, issued to Belnap et al on Oct. 29, 2013, covers an even more specific arrangement of layers and range of physical properties. U.S. Pat. No. 7,972,395, issued to Dadson on Mar. 13, 2014, discloses a system and method for processing a polycrystalline material with the specific recipe of the complexing agent.
It is an object of the present invention to provide a cutting element with thermal stability and toughness.
It is an object of the present invention to provide a cutting element with a balance of thermal stability and toughness in designated critical regions for extending the working life of the cutter.
It is another object of the present invention to provide a cutting element with a balance of thermal stability and toughness at a working edge of the cutting element to a worn edge of the cutting element.
It is an object of the present invention to provide a cutting element with a plurality of zones of different thermal stability and toughness.
It is another object of the present invention to provide a cutting element having zones of different metal content percentages.
It is still another object of the present invention to provide a cutting element having an arrangement of different metal content percentages in the diamond table.
It is an object of the present invention to provide a cutting element having an interrelationship of zones of different metal content percentages in the diamond table to affect working life.
It is an object of the present invention to provide a cutting element having an interrelationship of zones of different metal content percentages in the diamond table to account for cutting angle across the cutter.
It is an object of the present invention to provide a cutting element with a working life determined by wear resistance and impact resistance.
It is another object of the present invention to provide a cutting element with an interrelationship of zones of different metal content percentages in the diamond table setting wear resistance and impact resistance of the cutter.
These and other objectives and advantages of the present invention will become apparent from a reading of the attached specification.